Inorganic and Applied Chemistry

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Inorganic and Applied Chemistry

Many important chemical reactions involve oxidation and reduction. E.g. are the chemical reactions involved

in the production of energy typical redox-reactions. This also includes the conversion of food into energy in

the human body. Oxidation is defined as an increase of the oxidation level while reduction on the contrary is

defined as a decrease in the oxidation level explained in the following section.

6.1.1 Level of oxidation

In order to keep track of the number of electrons in a redox-reaction the so-called levels of oxidation are

introduced. They are defined from a certain set of rules defining how the electrons should be divided

between the components in the covalent bindings. We will look further into these rules below but first it is

necessary to recall the phenomenon of electro negativity. We saw earlier how different atoms have different

electro negativity meaning that the different atoms have different ability to attract electrons from other atoms.

This has also importance in respect to chemical bindings. As earlier presented the non-metals in the upper

corner of the periodic system have the best abilities to attract electrons. Examples of this are fluorine, oxygen,

nitrogen and chlorine. The orders for these atoms are according to electro negativity as follows:

F > O > N * Cl

Fluorine has thereby the largest ability to attract electrons followed by oxygen, nitrogen and chlorine. Such

considerations have importance in respect to the rules for oxidation levels summarised here:

The oxidation level of a neutral atom/molecule is zero. E.g. is the oxidation level of H 2 (g) and Na(s)

both zero.

The oxidation level of a mono atomic ion is the same as the charge. Thereby the oxidation level of

the Na+ ion +1 while it is -1 for the Cl- ion.

In covalent compounds with non-metals the hydrogen is given an oxidation level of +1. This means

that in the following compounds the oxidation level for hydrogen all are +1 per hydrogen atom: HCl,

NH 3 and H 2 O. Thereby the oxidation level is -1 for Cl in HCl, -3 for N in NH 3 and -2 for O in H 2 O.

Oxygen is given the oxidation level -2 in covalent compounds as e.g. in CO, CO 2 and SO 3. the only

exception from this rule is in peroxide compounds (containing the O 2 2- group) as e.g. H 2 O 2 where

each of the oxygen atoms is given the level of -1.

In binary compounds the atom with the largest electro negativity is given the oxidation level of its

negative charge. E.g. is flour always given the oxidation level of -1 while nitrogen typically is given

the level of -3 and sulphur typically -2.

The sum of the oxidation levels must be zero for an un-charged compound. E.g. must the sum of

oxidation levels for hydrogen and oxygen be zero in H 2 O while the sum of oxidation level must be

+1 in compounds as NH 4 + and similarly -2 in compounds as CO 3 2-.

Electrochemistry